1. Field of the Invention
This invention relates to the aerobic biodegration of contaminants in waste water by means of a rotating disk contactor.
2. Description of the Prior Act
The partial oxidation of distillate hydrocarbons to produce a gaseous mixture of hydrogen and carbon monoxide in the synthesis gas process is well known. According to this process, a carbonaceous gas or a distillate fuel, such as fuel oil, naphtha, methane, propane and refinery off-gases, and an oxygen-rich gas are introduced into a free-flow, non-catalytic synthesis gas generator at a temperature in the range from about 1500.degree. to 3000.degree. F. and a pressure in the range of about 1 to 250 atmospheres to effect the partial oxidation of the carbonaceous fuel to a synthesis gas stream comprising a mixture of hydrogen, carbon monoxide, carbon dioxide and water together with relatively minor amounts of hydrogen sulfide, carbonyl sulfide, argon, nitrogen, cyanide, ammonia and methane. Water is used as a quench medium to cool the synthesis gas produced in the generator. After the separation of the synthesis gas and a major proportion of the volatile by-product gases, such as CO.sub.2 and H.sub.2 S, from the quench water, a waste water stream remains containing small amounts of cyanides, formates and other by-products of the reaction. While this waste water stream contains toxic by-products of the synthesis gas process, it is, nevertheless, suitable as a recycle stream for the process either in admixture with the feed to the synthesis gas generator or as the quench medium to cool the hot synthesis gas mixture issuing from the gas generator. No waste water disposal problem occurs when the waste water stream can be continuously recycled in the synthesis gas process.
The reduced availability of natural gas and of petroleum gases and distillates as feedstocks materials has led to intensive efforts to develop other carbonaceous materials as fuels in the synthesis gas process. Among the carbonaceous materials under intensive investigation are petroleum residuum, petroleum coke, subbituminous, bituminous and anthracite coal, lignite, shale, organic waste material, sewage sludge, crude oil residues, coke and liquified coal and coal fractions.
When the fuel employed in a synthesis gas process contains significant amounts of water-soluble salts, such as a halide of a metal or ammonia, these salts are transferred to the waste water together with the cyanides and the formates produced in the process. While the concentration levels of these impurities in the waste water remains low, the waste water or at least a portion thereof can be recycled to the synthesis gas process either to be mixed with the fuel feed to the generator or introduced into the quench zone of the generator to cool the hot gaseous product being produced. However, when the concentration levels of the impurities in the waste water are high or become high as a result of recycling, then a waste water stream must be withdrawn and disposed of. Since this waste water contains environmentally significant amounts of cyanides and formates, and at least one halide salt of a metal or ammonia, it is characterized as having toxic, oxygen demanding and corrosive properties. The toxicity of the cyanides and the biochemical oxygen demand (BOD) of the formates are well established.
A variety of materials of a carbonaceous nature may be employed as the feed material or fuel to a synthesis gas process as indicated above. The compositions of these materials as well as the by-products produced and the waste water stream from the process vary greatly. In certain instances the waste water will contain metals including such metals as nickel and the transition metals chromium and vanadium, as well as ammonia and sulfides in combination with the previously noted environmentally significant components of the waste water stream.
U.S. Pat. No. 4,211,646, incorporated herein by reference, relates to a process for removing cyanide, sulfide, ammonia, soot and insoluble metals in the scrubbing water from a partial oxidation process. Ferrous sulfate and lime addition, followed by clarification, filtration and steam stripping are employed.
As this reference indicates, aerobic biodegradation has been used to treat waste water to reduce formates. Steam stripping of ammonia adds an additional processing stage and the lime addition step is particularly troublesome because it can be hazardous to workmen, is messy and expensive.
There exists a need in the art to environmentally upgrade waste water streams, particularly blow down water from a partial oxidation process for the production of synthesis gas by the partial oxidation of a liquid hydrocarbon fuel, without going through a separate ammonia stripping stage and a lime addition stage to remove cyanides.